The present invention pertains to track-laying crawler vehicles, and more particularly, to means for reducing the noise generated by the drive sprocket assembly in such crawler vehicles.
It has been established that the major source of noise-producing vibration in track vehicles is in the track system. The vibration causes hull panel or frame resonances and internal noise levels which are extremely uncomfortable to personnel, and which can in some instances be dangerous. Tests have shown that a large portion of the noise generated in the track system can be attributed to an interaction of the track segments with the drive sprocket and with the bogey and idler wheels. The track segments are relatively wide, that is, long in the direction of their movement. Thus, the track segments cannot smoothly follow a change in the direction such as occurs when they are carried around the drive sprocket, under the bogey wheels and around the idler wheels. As a result, the track segments slap against the drive sprocket, bogey wheels and idler wheels, and produce torsional vibrations and displacement of the wheels, which in turn generate both noise, structure-borne vibration and wear problems. Engagement and disengagement of the sprocket teeth with the segments also produce force and torque variations on the sprocket hub.
A large amount of noise in the drive sprocket is due to chordal action which, in a conventional drive sprocket configuration, is generated by the track entering the sprocket at approximately the one o'clock position from the upper strand, wrapping counterclockwise around the sprocket, and exiting from the sprocket at the six-thirty o'clock position. As the track is carried around the sprocket, it cannot form a smooth arc (as could a belt) because of the rigid track shoes. Instead, the shoes form a part of a polygon, which is equivalent to a series of chords of a circle, hence the name chordal action. Chordal action causes the velocity and acceleration of entering and exiting track pins to vary in a cyclical manner. As a track pin arrives directly above the sprocket, its horizontal velocity is at a maximum and its vertical or radial velocity is zero. As the track pin moves around the drive sprocket the horizontal velocity is reduced, while the vertical downward velocity is increased. Because of the rapidity of the velocity changes and the massiveness of the track, considerable vertical impact forces are generated causing vibrations and noise.